Non-Hodgkin's lymphoma is characterized by the malignant growth of B lymphocytes. According to the American Cancer Society, an estimated 54,000 new cases will be diagnosed, 65% of which will be classified as intermediate- or high-grade lymphoma. Patients diagnosed with intermediate-grade lymphoma have an average survival rate of 2-5 years, and patients diagnosed with high-grade lymphoma survive an average of 6 months to 2 years after diagnosis.
Intermediate- and high-grade lymphomas are much more aggressive at the time of diagnosis than are low-grade lymphomas, where patients may survive an average of 5-7 years with conventional therapies. Intermediate- and high-grade lymphomas are often characterized by large extranodal bulky tumors and a large number of circulating cancer cells, which often infiltrate the bone marrow of the patient.
Conventional therapies have included chemotherapy and radiation, possibly accompanied by either autologous or allogeneic bone marrow or stem cell transplantation if a suitable doner is available, and if the bone marrow contains too many tumor cells upon harvesting. While patients often respond to conventional therapies, they usually relapse within several months.
A relatively new approach to treating non-Hodgkin's lymphoma has been to treat patients with a monoclonal antibody directed to a protein on the surface of cancerous B cells. The antibody may be conjugated to a toxin or radiolabel thereby affecting cell death after binding. Alternatively, an antibody may be engineered with human constant regions such that human antibody effector mechanisms are generated upon antibody binding which result in apoptosis or death of the cell.
One antibody currently being investigated for the treatment of intermediate- and high-grade lymphomas is ONCOLYM® (131I-Lym-1) (Techniclone Corp.), which is a murine IgG2a monoclonal antibody which recognizes the HLA-Drl 0 protein which is present on the surface of over 80% of lymphoma cells. Only 2% of normal B cells (noncancerous) express the HLA-Drl 0 molecule. ONCOLYM® IgG2a monoclonal antibody is conjugated to a Iodine-[131] (131I), a radioactive isotope of iodine which emits beta irradiation for a distance of several millimeters, and is thereby thought to be an effective approach to targeting the outer rim of tumors and halting the progression of bulky disease
However, a potential disadvantage in using ONCOLYM® IgG2a monoclonal antibody in advanced forms of non-Hodgkin's lymphoma is that such lymphomas are often characterized by bone marrow involvement. Thus, administration of a radiolabeled antibody to such patients often results in unwanted myelosuppression and damage to healthy progenitor cells.
It would be advantageous if alternative therapies and other monoclonal antibodies could be administered to patients with intermediate- and high-grade lymphomas which circumvent some of the deficiencies associated with current treatments and decrease the frequency of relapse.